STORAGE MEDIUM, TONE GENERATION ASSIGNING APPARATUS AND TONE GENERATION ASSIGNING METHOD

When a harmony function is on state, a generator determines a chord based on one or more notes of depressed keys in a chord kea area, automatically generates one or more additional notes having pitches which harmonizes the pitch of the note of the depressed key in a performance key area according to the determined chord, and inputs the “note of the pressed key in the performance key area+additional notes” to an assignment controller. The assignment controller assigns plural parts (timbres) to the inputted notes, and sounds the notes in timbres of the plural parts according to the assignment. That is, tone generation assignment process is performed regarding not only notes according to performance operation by a user but also automatically generated additional notes.